1. Field of the Invention
The invention relates to the field of flow measurement. The invention provides an improved apparatus for determining the flow through a fire protection and/or domestic water supply system. In particular, the invention provides a flow detection and measurement means for distinguishing typical domestic water flow from the fire protection flow caused by one or more sprinkler heads. The invention also allows use of a water softener or similar device with a multipurpose piping system ("MPS") by providing a bypass around the water softener to ensure sufficient water flow for fire protection means. The invention also provides simple and inexpensive devices to measure flow with minimal pressure drop.
2. Description of the Prior Art
It is well known to provide a means for enunciating an alarm when water flows through a fire protection system. Typical fire protection systems do not have significant water flow therethrough unless a sprinkler head is activated by a fire. Thus, the typical commercial system need only to detect whether or not flow is present, and if so, an alarm must be enunciated.
In application Ser. No. 09/098,976 filed on Jun. 17, 1998, for an Apparatus And Method For Multipurpose Residential Water Flow Fire Alarm, a method was disclosed which allows the same piping to be used for both domestic and fire protection needs. The method provided for a flow detection and measurement means which is capable of distinguishing typical domestic flow from fire protection flow caused by the operation of one or more sprinkler heads.
The National Fire Protection Association ("NFPA") has established standards for the design and operation of multi-purpose residential fire sprinkler systems. The standard is known as NFPA 13D, 1999 Ed. It defines a multipurpose piping system as "[a] piping system within dwellings and manufactured homes intended to serve both domestic and fire protection needs."
Typical commercial fire sprinkler systems utilize a water flow detector to provide an alarm means. When a flow of sufficient, minimal, volume is detected, typical commercial systems indicate an alarm condition. The only reason that water typically flows in commercial systems is activation of a sprinkler head. Therefore, in a typical commercial system an alarm means need only determine whether or not water is flowing.
In an MPS water regularly flows through the common piping. Flows occur to supply domestic needs within the residence. Whenever a sink, shower or toilet valve open, water flows in the MPS. Therefore, the alarm system used on typical commercial applications will not work for MPS because simply taking a shower would cause a typical commercial flow detector to alarm when used with an MPS.
In light of this problem, typical residential applications have two completely different piping systems: (1) a fire sprinkler piping system, and (2) a domestic piping system. This basically doubles the number of pipes and the amount of plumbing work which has to be performed in a typical residential application. The same set of piping could not previously be used for both systems because the flow alarm would send false signals every time domestic water was turned on. Alternatively, a residential application could use a fire detection system (i.e., electronic fire sensor system). However, a fire detection system does not alarm when water flows. Therefore, with a fire detection system and no flow alarm, the fire sprinklers could run for days, causing extensive water damage, while the home owner is away on vacation and no alarm would sound.
As noted above, U.S. patent application Ser. No. 09/098,976 filed Jun. 1, 1998, disclosed an APPARATUS AND METHOD FOR MULTIPURPOSE RESIDENTIAL WATER FLOW FIRE ALARM. The apparatus for use as a multipurpose residential fire suppression water flow alarm system disclosed in that application was comprised of a supply side for delivering water under pressure; a multipurpose piping system having a system side with common piping for delivering water from the supply side to a fire suppression side with one or more sprinkler heads and a domestic side for one or more domestic uses; a detecting means for detecting fire protection flow and for distinguishing that flow from a maximum domestic flow, the detecting means being disposed between the supply side and the system side; a drain test connection; and an alarm means. The method of utilizing the apparatus described above was also disclosed. One of the dependent claims from the above-noted application, claimed a detecting means comprised of an orifice plate through which water flows causing a differential pressure measured by a differential pressure switch so that the flow rate to the orifice plate is proportional to the differential pressure allowing a determination of flow rate based on the differential pressure measured.
It was disclosed that the flow detection means could utilize any number of well known flow measurement technologies, such as U.S. Pat. No. 5,288,469 to Otten et al. However, Otten's device would be less than optimal for the current application because, when fire protection flows are needed, it is desirable to have a flow measurement device which has minimal pressure drop. The Otten device incorporates both an orifice plate and a cone-shaped plug around which the water flows. The cone-shaped plug causes a greater pressure drop than the orifice plate alone. U.S. Pat. No. 5,419,203 to Carmichael discloses a device similar to the device disclosed by Otten. Otten utilizes the Hall effect to measure the displacement of a displacement piston having incorporated therein a magnet. Carmichael utilizes strain sensors to measure the strain caused by displacement of a cone-shaped plug biased by a spring member. As the flow increases, the cone-shaped plug displaces backwardly in reaction to the flow putting greater pressure on the spring and consequently, greater pressure on the pressure sensors incorporated in the device. The Otten and Carmichael devices have several common features, namely a chamber having an orifice plate and a plug-shaped device adapted to be deflected away from the orifice plate in proportion to the flow rate through the chamber. Both Otten and Carmichael have the same primary drawback for use in multipurpose residential systems, namely the substantial pressure drop across these devices. Therefore, there is a need for a flow detection and measurement means for use in an MPS which causes less pressure drop in such a system. At the same time, the means must be simple in both operation and concept so that it will be inexpensive to build and can be easily programed and calibrated in the field.
Critics of MPS systems have also noted that it is common for residential systems to incorporate a water softener or similar devices (such as filters, chlorination systems, UV purifiers and the like). Water softeners and similar devices can create substantial drops in system pressure such that the water supply flowing through a typical residential system may not be sufficient for fire protection needs. Therefore, there is a need for a bypass mechanism which will allow sufficient flow in fire protection situations to bypass the water softener to supply the fire protection needs.